The present invention relates to a transfer system of information for a rotary storage unit, e.g., a storage unit using a rotating storage medium such as a magnetic disk or a photo disk, and more specifically, to control of read and write operations of the information for the rotary storage unit, thereby increasing throughput of an entire information processing system.
Generally, in a large scale magnetic disk apparatus, a plurality of disk units, i.e., disk drive units are connected to a disk controller and to a host unit through it to commonly use it in many cases. In such an apparatus, there occurs a problem in that, when one of the disk units is operatively connected to the disk controller, a sector interrupt from another disk unit can not be easily accepted by the disk controller or the host unit.
Here, the term "a sector" means each portion of that circle of a track on the disk which is divided in a circular direction with a predetermined period. One record corresponds to one sector in a fixed-length record format and one record corresponds to one to a few sectors in a variable-length record format. The term "a sector interrupt" means a notice for informing to the disk controller or the host unit (to be referred to as a host side unit hereinafter) that a head of the disk unit reaches a target sector and a write or read operation can be performed for the target sector.
In order to dissolve the above problem, a conventional method, as is disclosed in Japanese Patent Unexamined Publication JP-A-62-145569, is known. In the method, a counter is provided in the disk controller in correspondence with each disk unit, and when a RPS (disk rotation position sensing) interrupt, e.g., a sector interrupt is not informed from one of the drive units to the host side unit in spite of exceeding a predetermined value set in a corresponding counter because the RPS interrupts are generated from other disk units, the sector interrupt from the drive unit is given the highest priority to be informed to the host side unit by changing a timing when the sector interrupt is generated.
In addition, another method for dissolving the above problem is disclosed in Japanese Examined Patent Publication JP-B-62-3455. In this method, in a case where information is to be read out from a disk and to be transferred to a host side unit, the read out information is stored in a buffer memory provided for each disk unit if a disk controller is so busy that it cannot be operatively connected to the disk unit when a sector interrupt is generated to the disk controller by the disk unit, and the information stored in the buffer memory is transferred to the disk controller when it is not busy. In contrary, in a case where information is to be written from the host side unit such as the disk controller or a host unit into the disk, the information from the host side unit is temporarily stored in the buffer memory and written in the disk after a read/write section in the disk unit reaches a predesignated rotation position on the disk, i.e., a target sector.
However, the following two problems are in the conventional method disclosed in the above JP-A-62-145569. First, changing the timing when the sector interrupt is generated means that the sector interrupt is generated at a timing shifted from an optimal timing. Therefore, the throughput of the entire system is decreased.
Second, the above conventional method cannot be applied to a system employing a large scale disk apparatus, wherein, in the apparatus, two disk controllers (to be referred to as controllers hereinafter) are connected to a plurality of disk units (to be referred to as rotary storage units hereinafter), a sector interrupt from one of the rotary storage units is informed to a host unit through one of the controllers which is not busy, and thereby the throughput of the system is increased (see Japanese Unexamined Patent Publication, JP-A-54-146941).
With the conventional method disclosed in the above JP-A-62-3455, there are the following four problems:
First, in the method, when it is detected that a rotary storage unit cannot be operatively connected to the controller, i.e., that the controller is busy, the rotary storage unit continues to store or starts to store information read out from a predesignated sector by the rotary storage unit in the buffer memory (to be referred to as the buffer hereinafter). Therefore, there is a case where a write operation on the information from the sector into the buffer by the rotary storage unit is not yet completed in spite of rotation of the disk for one or more cycles after the read section is positioned on the predesignated sector. In this case, the information must be transferred from the buffer to the controller after the write operation of the information from the sector is completed. As a result, the method requires a long rotation waiting time until the disk is rotated for one or more cycles after the positioning operation is completed. Second, in the method, a read section for reading out information from a rotary storage unit without a read/write command from the controller is not taken account for. That is, in the conventional method, a read/write operation is not started immediately when a seek operation by the read/write section (the head) is completed so as to position or track the head on a target track but performed in response to the read/write command for a predetermined sector when a rotating storage medium is rotated to a predetermined position relative to the head.
Second, there is no description concerning means for reading out the information from the rotary storage unit without a read or write command from the controller. More specifically, in the conventional method, the read or write operation is not started immediately after a seek operation of the read/write section (a head) is completed so as to position or "on-track" the head on a target track but started when the head reaches a target sector after a read or write command for the target sector is received from the controller.
Third, only the effect in that performance of a computer system is increased by buffering the information when the controller is busy can be obtained. That is, increase in a data transfer rate, decrease in the waiting time unitl the desired data is obtained, or the like are not taken account for.
A first object of the present invention is to provide an information transfer control system, having a rotary storage unit, in which data from arbitrary rotation position can be read out without a rotation waiting time after a head is positioned on a desired cylinder or track.
A second object of the present invention is to provide a disk control system in which data can be read out from a rotary storage unit without receiving a read command from the controller, wherein data is read out at the same time from a plurality of tracks defined by a common cylinder on a plurality of disks, so that any data other than data recorded on a track designated by the upper device can also be transferred to the upper devices without waiting for positioning of the head on the track.